The invention relates to the genetic manipulation of plants, particularly to transforming plants with genes that enhance disease resistance.
Throughout their lives, plants are routinely subjected to a variety of stresses, which act to impede or alter growth and development processes. Stresses to plants may be caused by both biotic and abiotic agents. For example, biotic causes of stress include infection with a pathogen, insect feeding, and parasitism by another plant such as mistletoe, and even grazing by ruminant animals. Abiotic stresses include osmotic stress, excessive light intensity or insufficient light intensity, cold temperatures, warm temperatures, synthetic chemicals such as those used in agriculture, and excessive wind.
Because a stress negatively impacts plant growth and development processes, stress to agricultural plants has a negative economic impact expressed in the form of reduced yields, increased expenditures for pesticides, or both. Developing crop plants that are better able to tolerate or even avoid stresses is desirable and will most certainly improve agricultural productivity. Given the world""s both increasing human population and diminishing land area available for agriculture, improving agricultural productivity is a paramount challenge. A thorough understanding of the mechanisms used by plants to avoid or tolerate stresses may help in the development of new strategies of improving the stress tolerance of agricultural plants.
In spite of the great frequency of stresses, plants survive, and often flourish. Plants are able to do this because of the evolution of a variety of internal and external mechanisms for avoiding or tolerating stress. For example, higher plants possess leaves with waxy, water-impermeable surfaces and pores known as stomata, which serve to allow the escape of water vapor during the process of transpiration. The periphery of the stomatal pores is lined with a pair of cells known as guard cells, which control the aperture of the pore. By modifying their size and shape through a turgor-pressure-mediated process, the guard cells can completely block the pore when conditions are unfavorable for transpiration during, for example, periods of low soil-water availability. Such a stress-avoidance system allows a plant to survive conditions of water stress by reducing transpiration to nearly zero and preventing dehydration.
Plants also possess defense systems which prevent or help limit the stresses resulting from attacks by pathogens and insects. One well-known defense system against plant pathogens is known as systemic acquired resistance. Another defense system is the systemic induction of proteinase inhibitors following insect damage, which is usually referred to as the systemic wound response. In both of these defense systems, the initial impact of the pathogen or insect is transmitted via a signal or signals to other parts of the plant, resulting in the increased expression of genes encoding proteins that are directly or indirectly inhibitory to the invading organism. The associated, systemic increase in defense gene products is known to increase the resistance of the plant to both current and future stresses from pathogens and insects.
While certain components of the systems that plants use to respond to abiotic and biotic stresses are known, most components have yet to be elucidated. Uncovering the genetic components of such systems will provide plant breeders with new targets for crop improvement strategies.
Methods and compositions for expressing defense-related, signaling genes are provided. The compositions comprise nucleotide sequences from defense-related, signaling genes isolated from sunflower. The nucleotide sequences of the invention relate to sunflower genes encoding a neoxanthin cleavage enzyme (NCE), an amino acid permease (AAP) and a novel glutamic acid-rich protein designated GRP (previously designated GPR). The compositions of the invention find use in agriculture, particularly in methods for increasing the resistance of plants to pathogens, methods for modifying abscisic acid metabolism in a plant, methods for modifying amino acid transport in a plant, and methods for modifying the amino acid content of a plant. The methods comprise stably transforming the genome of a plant with nucleotide sequences of the invention operably linked to a promoter that drives expression in a plant cell.
Methods for regulating gene expression in plants are provided. The methods comprise stably transforming a plant with a DNA construct comprising a promoter from either a sunflower NCE gene or a sunflower GRP gene operably linked to a second nucleotide sequence. Methods involving a promoter from the NCE gene find use in modulating the expression of a gene in a plant in response to pathogens, oxidative stress, oxidants, and defense-related signaling molecules such as, for example, jasmonic acid and salicylic acid. Methods involving a promoter from the GRP gene find use in preferentially expressing a gene in a plant stems.
Expression cassettes comprising sequences of the invention are provided. Additionally provided are transformed plants, plant tissues, plant cells, and seeds thereof. Isolated proteins encoded by the sequences of the invention are also provided.